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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

82

POTASSIUM CHLORATE

or hydrogen sulphide) and normal barium chloride solution added in amount
exactly equivalent to the potassium sulphate (also to any phosphate present)
already found by another way. The liquid is heated and filtered, the
insoluble matter washed, the filtrate evaporated to dryncss and the residue
carefully ignited, taken up in a little water and a few drops of ammonium
carbonate, the solution filtered if necessary and evaporated in a tared
platinum dish, the residue being gently ignited and weighed. In the pure
chlorides thus obtained the chlorine is determined volimietrically by Vol-
hard's method and the chlorides of sodium and potassium calculated (sea
Stassfurt Salts, Determination of sodium chloride). A better method
(especially if the sodium is in small amount) is to determine the potassium
as platinichloride or perclilorate and to calculate by difference the sodium
chloride, which is then expressed as carbonate : NaCl X 0-906 -™ NaaC03.

Crude potassium carbomvte usually contains 50-90% of K./'X"),,, with vary-
ing proportions of water, insoluble substances, sulphate, chloride, etc. In some
crude potashes a,s much as (>o% of sodium carbonate occurs, but the best: qualities
contain about 2%.

The commercial pure carbonate, from Sl.assi'uri. salts, contains 90-98%
K2COa, and the less pure forms from molasses 92% K2CO., with more or less
considerable proportions of phosphate, often caustic potash ami sulphur and
cyanogen compounds, and sodium, carbonate (t>>o5~'2\e5%)1 potassium chloride
(o'5-2'5%), and potassium sulphate (<^5"3%)-

The chemically pure carbonate may still contain traces of chloride and sul-
phate.

POTASSIUM   CHLORATE
KC10., ^ 122-56 (122-5)

Colourless, odourless crystals soluble in about. 16 parts of cold water;
when heated it fuses and evolves oxygen. It is usually met with in the
pure, state, but it. may contain small, quantities of chlorides, hypoehlorites,
sulphates, arsenic, lead, iron and lime. Adulterations with nitre, potassium
chloride, boric acid and mica have been detected. These impurities may
be discovered by the following tests and the chlorate1 determined as in 7.

1.  Chlorides, Sulphates.—The 1:20 solution is tested with silver
nitrate or barium chloride.

2.  Hypochlorites.-......-The i : 20 solution should give no immediate blue

coloration with potassium iodide and starch paste, in the, cold, but the pure
chlorate yields a faint blue after some minutes.

3.  Nitrates,.............i gram, heated with 5 e.e, of sodium hydroxide solution,

0-5 grams of iron turnings and 0-5 gram of mic dust, should not evolve
ammonia.

4.  Metals,  Alkaline Earths,—-The   r : 20 solution  is treated with
hydrogen sulphide or ammonia and ammonium sulphide or ammonium
oxalate:   no turbidity should appear.

5.  Arsenic.~i gram is strongly heated to transform it into chloride
and then tested in the Marsh apparatus (sec Flesh Foods, Vol. II).

6.  Boric Acid, Mica.- -The. .sample is treated with 96% alcohol and
filtered, the; filtrate being tested for boric acid by burning the alcohol (greendichromate in the solution determined iodometrically. XV, z, p, 32j, and Hull, chim. /arm,,